Centrifugal switch for motion picture projecting machines



Jan. 26, 1932. T. T. ALLEN ET AL 1,842,644

CENTRIFUGAL SWITCH FOR MOTION PICTURE PROJECTING MACHINES Filed Oct. 1, 1927 4 Sheets-Sheet 1 WITNESS W5 fifmfi'amisjdams, BY I I. L

ATTORNEY Jan. 26, 1932. ALLEN ET AL 1,842,644

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Patented Jan. 26, 1932 UNITED STATES PATENT OFFICE THOMAS '1. ALLEN AND JOHN FRANCIS ADAMS, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNORS 'I'O SENTRY SAFETY CONTROL CORPORATION, OF PHILADELPHIA,

PENNSYLVANIA OENTRIF'UGAL SWITCH FOR MOTION PICTURE PROJECTING MACHINES Application filed October 1, 1927.

Our invention relates to a centrifugal switch for use as an automatic control apparatus for motion picture projecting machines, and more particularly to a device which may .6 be used in conjunction with an apparatus adapted to stop the projecting mechanism and intercept the rays of light passing through the film whenever the film fails to move through the path of therays of light.

If the speed of the film moving through the projecting mechanism falls below a certain number of feet per minute, the images are not projected upon the screen in rapid enough succession to give the illusion of continuous movement and this result is highly unsatisfactory to the audience viewing the picture. If the film should move very slowly through the projecting mechanism, it would be subjected to heat from the lamp for too long a period and might'ignite and cause a fire.

One of the objects of our invention is to provide a device adapted to be connected to a rotatable part of a projecting machine and to open and close an electric circuit at different speeds of such rotating part.

Another object is to provide a centrifugal switch of this character having improved means for regulating the speed at which it will open or close an electric circuit.

Still another object is to provide means of this character having a peculiar arrangement of swingable and fixed contacts which renders the same highly sensitive and particularly adapted for the control of film speed.

According to the invention the centrifugal switch has a normally stationary shaft, a normally stationary part and a rotatable part mounted on said shaft, the rotatable part being operatively connected to a rotatable part of the machine with which the centrifugal switch is used, terminals on the stationary part, pivotally mounted contacts on the retatable part, and means yieldably holding said contacts engaged with the said terminals and adapted to be overcome by centrifugal force'when the rotatable part is operated at a predetermined speed to thus break the electrical connection between said contacts and terminals.

The drawings illustrate embodiments of Serial No. 223,306.

the invention as well as the wiring diagram showing the incorporation of the switch in fire prevention mechanism of a motion picture machine, together with the electrical connections, and the views in the drawings are as 5 follows Figure 1 is a front view of a fragment of a projecting machine upon which an embodiment of our invention has been installed, and

Figure 2 a central longitudinal sectional view through the embodiment shown in F igure 1, as indicated by the line 2-2' on that figure,

Figure 3 is an enlarged perspective view of one of the fixed contacts,

Figure 4 aperspective View of the saddle in which the swingable contacts are mounted, and

Figure 5 a perspective viewof a bracket for adapting the embodiment shown in Figure 5 l to a different type of projecting machine.

Figure 6 is a central vertical longitudinal sectional view through another embodiment of our invention,

Figure 7 a cross-sectional View thereof, as indicated by line 77 on Figure 6,

Figure 8 a cross-sectional view looking in the opposite direction, as indicated by the line 88 on Figure 6, and

Figure 9 a sectional plan View of the device, as indicated by the line 99 on Figure 6.

Figure 10 is a perspective view of a fragment of a. projecting machine, different from that shown in Figure 1, and illustrates the application of the switch of Figs. 6 and 9 thereto.

Referring first to the embodiment shown in Figures 1, 2, 8 and 4, the device is provided with a casing 12 of nonconducting material having a hub 13 through which a shaft 14 is threaded. A head 15 of insulating material is secured in casing 12 in any suitable manner, as by screws 16, and has embedded in its outer surface a pair of substantially semi-circular fixed contacts 17 provided with anchors 18 and 19 which extend through head 15. Anchors 19 are provided with apertures 20 so that an electric wire 21 may be attached to either anchor 19 of one 199 contact while a second electric wire 22 (see Figure 11) may be connected to one of the anchors 19 on the other fixed contact 17; the two fixed contacts being separated from one another so that the electric circuit, of which wires 21 and 22 form parts, is broken at this point.

Shaft 14 is slidable and rotatable in head 15 and provided with a shoulder 23 adjacent the forward face of head 15 so that a reduced portion is formed upon which a sleeve 24 is rotatably mounted and held against shoulder 23 by a nut 25 threaded onto the outer end of shaft 14 and adapted to be held against rotation by a set screw 26. A disk 27 and a gear 28, both of insulating material, are fixed on sleeve 24 and adapted to be rotated by a gear meshing with gear 28 and rotated by or forming a part of the projecting mechanism.

A saddle 29 is secured to or embedded in the inner face of disk 27 and may be further held against dislodgment by screws 30 passing through gear 28 and disk 27 and thieaded in the apertures 31 formed in saddle 29; screws 30 also holding disk 27 and gear 28 together. As saddle 29 is, at times, connected into an electric circuit, the heads of screws 30 are guarded by a thin insulating disk 32 secured to the outer face of gear 28 in any suitable manner, as by screws 33.

A fork 34 is formed on each end of saddle 29 and has swingably mounted therein an L-shaped contact 35 which may be of ordinary conducting material or provided also with a contact point 36 of highly conducting material. Springs 37 are mounted in wells formed in disk 27 and engage the undersides of contacts 35, yieldingly holding them against fixed contacts 17.

In mounting the device on the type of projecting machine shown in Figure 1, a bracket plate 38 is secured to the machine by passing screws 39 through the plate and threading them into holes existing in the machine. The end of shaft 14 is mounted in the bore'of a boss 40 formed on bracket plate 38 and held therein by a set screw 41 threaded through one wall of boss 40 and extending into an annular groove 42 formed in shaft 14, for holding the shaft against longitudinal movement, and engaging the shaft and hold ing same against rotation.

A gear 43 is mounted on the shutter shaft 44 of the projecting machine and secured in place by a set screw 45 so that, as shutter shaft 44 revolves, gear 28 and disk 27 will be rotated, causing contacts 35 to depress springs 37 by the influence of the centrifugal force thus produced and open the electrical circuit at this point; casing 12 being held against rotation on shaft 14 by a set screw 46 threaded through hub 13 and engaging the threaded portion of shaft 14.

As the speed of rotation at which contacts 35 will swing away from contacts 17 depends upon the tension of springs 37, it is necessary to provide an adjustment of the tension of these springs in order to regulate the device to break the circuit at any desired speed of shutter shaft 44. T 0 make such an adjustment, set screws 41 and 46 are loosened, casing 12 held against rotation, and shaft 14 turned in one direction or the other to bring disk 27 closer to, or farther from head 15, consequently increasing or decreasing the tension e51 springs 37 when the device is standing 1 e.

The device shown in Figures 6 to 9 is adapted to be mounted by means of a bracket 55 provided at one end with slots 56, through which bolts are passed and threaded into holes provided for same, and at its other end with a flange 57 and a transverse guideway 58. A screw 59, rotatable in flange 57 and held against axial movement by a collar 60, is threaded into a guide 61 slidable in guidewa 58 and forming a part of the casing 62. head 63 is fixed in casing 62 and provided with a pair of substantially semi-circular fixed contacts 64 which are separated from one another, as plainly shown in Figure 8, and to which are attached the ends of wires 21 and 22 when this embodiment of our invention is used as shown in that figure.

A shouldered shaft 65, secured in flange 57 and locked in position by a nut 66, has a gear 67 and a disk 68 rotatably mounted thereon and held against axial movement by a head 69 formed on shaft 65; gear 67 and disk 68 being fixed to one another in any suitable manner as by screws 70. A pair of swinging contacts 72 are hinged in a pair of saddles 73 secured to the face of disk 68 and electrically connected to one another by a wire 74. Tension springs 75 are mounted in suitable wells formed in disk 68 and abut the underside of contacts 72 and yieldingly hold them against fixed contacts 64 and complete the electric circuit when disk 68 is not rotating.

When the device is mounted on a projecting machine so that gear 67 meshes with gear 50, as shown in Figure 10, disk 68 will be rotated and contacts 72 swung away from contacts 64 against the action of springs 75 so as to open the circuit at this point. The speed at which contacts 72 will swing away from contacts 64 is dependent upon the tension of springs 75 and this tension is adjusted by rotating screw 59 so as to slide casing 62 in one direction or the other in guideway 58, thus moving disk 68 toward or from head 63.

Of course the centrifugal switch as illustrated may be modified and changed in various ways without departing from the invention herein set forth and hereafter claimed.

We claim:

1. A centrifugal switch including a normally stationary part, a pair of terminals spaced from one another on the stationary part, a rotatable part, contacts hinged thereon and adapted to engage the terminals, springs tending to hold the arms against swinging, and a conductor electrically connecting the arms.

2. A centrifugal switch including a stationary casing, stationary contacts in the casing, a rotatable part, saddles on the rotatable part, contacts swingable in the saddles, means tending to hold the swingable contacts against the stationary contacts, and means for rotating the rotatable part.

3. A centrifugal switch comprising a normally stationary shaft, a normally stationary part and a rotatable part mounted on said shaft, a pair of terminals on the stationary part, pivotally mounted contacts on the rotatable part, and means yieldably holding said contacts engaged with said terminals and adapted to be overcome by centrifugal force when the rotatable part is operated at a predetermined speed to thus break the electrical connection between the contacts and said terminals.

4. A centrifugal switch comprising a normally stationary shaft, a normally stationary part and a rotatable part mounted on said shaft, a pair of terminals on the stationary part, pivotally mounted contacts on the rotatable part, and spiral springs yieldably holding said contacts engaged with said terminals and adapted to be compressed by centrifugal force when the rotatable part is operated at a predetermined speed to break the electrical connection between said contacts and said terminals.

5. A centrifugal switch comprising a normally stationary shaft, a normally stationary part and a rotatable part mounted on said shaft, a pair of terminals on the stationary part, pivotally mounted contacts on the rotatable part, spiral springs yieldably holding said contacts engaged with said terminals and adapted to be compressed by centrifugal force when the rotatable part is rotated at a predetermined speed to break the electrical connection between said contacts and said terminals, and means for changing the relative position of said stationary part and rotatable part whereby the speed of the rotatable part necessary to produce suflicient centrifugal force to break the connection between said contacts and terminals may be regulated at will.

In testimony whereof we have signed our names to this specification.

THOMAS T. ALLEN. JOHN FRANCIS ADAMS, 

